The present application claims priority to Japanese Application No. 11-103236 filed Apr. 9, 1999 which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a magnetic head unit having a rotary drum in which a magnetic head element is disposed and to a method for writing or reading signals to/from a magnetic tape by using the magnetic head unit.
2. Description of the Related Art
Hitherto, there has been proposed a helical scan type signal recording/reproducing method for recording/reproducing signals to/from a magnetic tape by obliquely sliding a magnetic head element mounted in a rotary drum on the running magnetic tape.
Because this helical scan method is a method for writing or reading signals by sliding the magnetic head element on the running magnetic tape at high speed, it has merits that the relative sliding speed of the magnetic tape and the magnetic head element is fast and that a high data transfer rate may be obtained.
The magnetic head unit for writing or reading signals to/from the magnetic tape by means of this helical scan method comprises a unit body whose outer shape is approximately cylindrical and the magnetic head element attached to the rotary drum side of the unit body. The magnetic head element is attached to a head base such that its edge portion is fixed to the rotary drum so that it projects somewhat out of the peripheral plane of the unit body. Meanwhile, the magnetic tape is wound around the peripheral plane of the unit body while slanting by a predetermined slant angle with respect to the direction which crosses at right angles with an axis of rotation of the rotary drum, e.g., by a winding angle of 180 degrees.
The magnetic head element attached to the rotary drum slides aslant on the magnetic tape, thus writing or reading signals to/from the magnetic tape, when the rotary drum is rotated while winding the magnetic tape around the peripheral plane of the unit body.
By the way, the condition of contact between the magnetic head element of the magnetic head unit and the magnetic tape depends on a projection of the edge portion of the magnetic head element out of the peripheral plane of the unit body. Then, when the edge portion of the magnetic head element projects too much out of the peripheral plane of the unit body, the pressure of contact of the magnetic head element to the magnetic tape becomes excessive, thus becoming a factor of increasing the wear of the magnetic head element or of damaging the magnetic tape. When the edge portion of the magnetic head element projects too little out of the peripheral plane of the unit body on the contrary, the magnetic head element does not touch the magnetic tape well, thus causing a large spacing loss produced by a gap between the magnetic head element and the magnetic tape to decrease the output.
By the way, the adoption of a magneto-resistance effect type magnetic head element as a reproducing magnetic head element has been discussed in order to deal with the recent requirement for recording at high density by the helical scan method magnetic head unit.
Although the magneto-resistance effect type magnetic head element has a merit that it allows a high reproducing output to be obtained as compared to an inductive type magnetic head element which has been used in general as a reproducing magnetic head element in the helical scan method magnetic head unit, it has had a problem that it is very liable to wear when it is slid on a magnetic tape at high speed.
Then, in the magnetic head unit described above, the magneto-resistance effect type magnetic head element must be attached to the rotary drum more carefully and the projection of the edge portion of the magnetic head element from the peripheral plane of the unit body must be adjusted at higher precision to minimize the wear of the magnetic head element when it is adopted as the reproducing magnetic head element.
However, it is very difficult and cumbersome to adjust the projection of the edge portion of the magnetic head element out of the peripheral plane of the unit body in the stage of attaching the magnetic head element to the rotary drum, as described above.
Further, even if the magnetic head element is attached to the rotary drum such that the projection of the edge portion of the magnetic head element out of the peripheral plane of the unit body is optimized, it is unable to avoid the advancement of the wear of the magnetic head element which occurs along its use. Then, when the magnetic head element is attached fixedly to the rotary drum like the magnetic head unit described above, the projection of the edge portion of the magnetic head element out of the peripheral plane of the unit body changes and the touch of the magnetic head element to the magnetic tape may not be kept well when the wear of the magnetic head element advances.
Because the magnetic tape is wound aslant around the peripheral plane of the unit body in the magnetic head unit described above, the ratio of a part of the magnetic tape wound around the rotary drum to a part of the magnetic tape wound around the stationary drum differs depending on the position. For instance, the magnetic tape is wound more to the rotary drum at the tape advancing side of the unit body, i.e., at the side where the magnetic tape is started to be wound, and the magnetic tape is wound more to the stationary drum at the side of the unit body where the tape is released.
Then, in the magnetic head unit, air film is created between the rotary drum and the magnetic tape as the rotary drum is rotated, and the distance between the magnetic tape and the peripheral plane of the unit body differs corresponding to the rate of the part of the magnetic tape wound to the rotary drum. That is, the distance of the magnetic tape at the part wound more to the rotary drum from the peripheral plane of the unit body is large than the magnetic tape of the part wound more to the stationary drum. Accordingly, when the magnetic head element is fixed to the rotary drum like the magnetic head unit described above, the pressure of contact of the magnetic head element to the magnetic tape changes depending on the position of the magnetic tape where the magnetic head element slides, i.e., whether the magnetic head element is located at the side where the magnetic tape advances or at the side where the magnetic tape is leased, thus causing nonuniformity of the touch in some cases.
The present invention has been made in view of the problems as described above and provides a magnetic head unit which is arranged so as to effectively suppress the wear of the magnetic head element and the damage of the magnetic tape and to be able to obtain a high output by keeping the touch of a magnetic head element to a magnetic tape well, and a method for writing or reading signals by using the magnetic head unit.
According to one aspect of the invention, the magnetic head unit comprises an approximately cylindrical unit body having a stationary drum and a rotary drum turnably provided with respect to the stationary drum; a magnetic head element in which an edge portion thereof is disposed in the rotary drum side so as to face to the outside from the peripheral plane of the unit body; and head projection regulating means for varying a projection of the edge portion of the magnetic head element out of the peripheral plane of the unit body.
In this magnetic head unit, the unit body has the rotary drum and the stationary drum and is formed approximately into the cylindrical shape as a whole. The rotary drum is turnable with respect to the stationary drum.
The magnetic head element is disposed on the rotary drum side of the unit body. The magnetic head element is provided such that the edge portion thereof faces to the outside from the peripheral plane of the unit body. When the rotary drum is rotated, the magnetic head element slides on a magnetic tape wound around the peripheral plane of the unit body, thus writing or reading signals to/from the magnetic tape.
In the magnetic head unit, the head projection regulating means is configured so as to be able to change the projection of the edge portion of the magnetic head element out of the peripheral plane of the unit body. The head projection regulating means is composed of a piezoelectric ceramic provided between the rotary drum and the magnetic head element for example.
The magnetic head unit can keep the touch of the magnetic head element to the magnetic tape always well as the head projection regulating means changes the projection of the edge portion of the magnetic head element out of the peripheral plane of the unit body in correspondence to the state of the magnetic head element and to the fluctuation of distance between the magnetic tape and the peripheral plane of the unit body.
Preferably, the head projection regulating means changes the projection of the edge portion of the magnetic head element in synchronism with the rotation of the rotary drum so that the projection of the edge portion of the magnetic head element differs at the sliding starting side where the magnetic head element starts to slide with respect to a magnetic tape which runs along the peripheral plane of the unit body and at the sliding ending side where the magnetic head element ends to slide with respect to the magnetic tape.
The touch of the magnetic head element to the magnetic tape may be kept at the good condition by the head projection regulating means, even when the distance between the magnetic tape and the peripheral plane of the unit body differs at the sliding starting side and the sliding ending side in correspondence to the ratio of the part of the magnetic tape wound around the rotary drum for example, by changing the projection of the edge portion of the magnetic head element in synchronism with the rotation of the rotary drum so that the projection of the edge portion of the magnetic head element differs at the sliding starting side and the sliding ending side.
Further, driving electric power for driving the head projection regulating means is preferably transmitted in AC via a non-contact type signal transmitter provided between the stationary drum and the rotary drum for transmitting signals between the magnetic head element disposed on the rotary drum side and the stationary drum side.
Then, no transmitter needs to be provided anew for transmitting the driving electric power for driving the head projection regulating means, by transmitting the driving electric power for driving the head projection regulating means via the non-contact type signal transmitter provided for transmitting signals between the magnetic head element disposed on the rotary drum side and the stationary drum side, and the structure may be simplified.
Still more, a magneto-resistance effect type magnetic head element is preferably used as the magnetic-head element in the magnetic head unit. Thereby, the magnetic head unit can improve the reproduced output. It is noted that the driving electric power for driving the magneto-resistance effect type magnetic head element is preferably transmitted in AC via the non-contact type signal transmitter described above. Thereby, the structure of the magnetic head unit may be simplified.
According to another aspect of the invention, in a method for writing or reading signals to/from a magnetic tape by sliding a magnetic head element whose edge portion is disposed on the rotary drum side so as to face to the outside from the peripheral plane of an approximately cylindrical magnetic head unit by running the magnetic tape along the peripheral plane of the magnetic head element having a stationary drum and a rotary drum turnably provided with respect to the stationary drum and by rotating the rotary drum, the method is characterized in that signals are written/read to/from the magnetic tape while changing the projection of the edge portion of the magnetic head element from the peripheral plane of the magnetic head unit in synchronism with the rotation of the rotary drum.
According to this method for writing or reading signals, the projection of the edge portion of the magnetic head element out of the peripheral plane of the magnetic head unit is changed in synchronism with the rotation of the rotary drum, so that the touch of the magnetic head element to the magnetic tape may be kept always at good condition and the signals may be appropriately written/read to/from the magnetic tape even when the distance between the magnetic tape and the peripheral plane of the unit body fluctuates due to the rotation of the rotary drum.
It is noted that in this method for writing or reading signals, the projection of the edge portion of the magnetic head element is changed in synchronism with the rotation of the rotary drum so that the projection of the edge portion of the magnetic head element changes at the sliding starting side where the magnetic head element starts to slide with respect to the magnetic tape and the sliding ending side where the magnetic head element ends to slide with respect to the magnetic tape. Thereby, the touch of the magnetic head element to the magnetic tape may be kept at good condition and the signals may be written/read to/from the magnetic tape even when the distance between the magnetic tape and the peripheral plane of the unit body differs at the sliding starting side and the sliding ending side corresponding to the ratio of the part of the magnetic tape wound around the rotary drum.
Further, in this method for writing or reading signals, it is desirable to transmit the driving electric power for changing the projection of the edge portion of the magnetic head element in AC via a non-contact type signal transmitter for transmitting signals between the magnetic head element disposed on the rotary drum side of the magnetic head unit and the stationary drum side.
Then, no transmitter needs to be provided anew for transmitting the driving electric power for changing the projection of the edge portion of the magnetic head element, by transmitting the driving electric power for changing the projection of the edge portion of the magnetic head element by the non-contact type signal transmitter provided to transmit signals between the magnetic head element disposed on the rotary drum side and the stationary drum side, and the structure of the magnetic head unit may be simplified.
In this method for writing or reading signals, it is desirable to use a magneto-resistance effect type magnetic head element is used as the magnetic head element. Thereby, the reproduced output may be improved. It is noted that it is desirable to transmit the driving electric power for driving the magneto-resistance effect type magnetic head element in AC via a non-contact type signal transmitter described above. Thereby, the structure of the magnetic head unit may be simplified.
The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings.